A fossil reveals the secrets of one of nature’s most mysterious reptiles

New Zealand’s tuatara look like gloomy iguanas. But these spiny reptiles are not actually lizards. Instead, they are the last remnants of a mysterious and ancient order of reptiles known as Rhynchocephalians that mostly disappeared after their heyday in the Jurassic period.

And they are truly the peculiar balls of the family of reptiles. Tuataras can live for more than a century, inhabit cold climates and are capable of Move their jaws back and forth For cutting insects, sea birds and each other. Even they have a primitive third eye Under the scales on top of their heads that may help them keep track of the sun.

These strange traits make the tuatara an evolutionary mystery, and the sporadic fossil record of its long-lost relatives has baffled paleontologists. Likely to outpace lizards and snakes, nearly all of the Rhynchocephalians became extinct at the end of the Mesozoic era. Many left behind little more than fragments of a tooth and a jaw.

It turns out that an important piece of this puzzle has been in the museum’s drawer for decades. While sifting through a collection of accumulated fossils at Harvard University’s Museum of Comparative Zoology, Stephanie Pierce, curator of vertebrate palaeontology, and her team recently discovered the nearly complete skeleton of a lizard-like animal on a slab of stone small enough to fit in a palm. from their hands.

The remarkable fossil was discovered in 1982 during an expedition to the Kayenta Formation, a fossil-rich outcrop in northern Arizona. This band of red rock was deposited during the early Jurassic period when the era of dinosaurs was in its infancy. Around this primitive floodplain, early dinosaurs such as the crested Dilophosaurus mingled with powerful crocodile-like creatures encased in armor. Underfoot, primitive shrew-like mammals and this strange new reptile set off.

While the early mammal fossils at the site have received a lot of initial interest, Dr. Pierce and Thiago Simويسes, a Harvard postdoctoral paleontologist who specializes in the early evolution of lizards, finally studied this specimen in depth.

In an article published Thursday in Communication BiologyScientists have named the new animal Navajosphenodon sani. Both the genus and species name (which means “old age” in the Navajo language) refer to the Navajo tribe, who lived in the area where the fossil was found.

The scientists used computed tomography scans to examine the mashed-up fossil in three dimensions and digitally assemble the skull flattened like a puzzle.

Although his body was lizard-like, the structure of his skull resembled a tuatara. It possessed similar rows of sharp, interlocking teeth extending directly from the jawbone. The skull also has two openings behind the animal’s eye. This formation is one of the main features that distinguishes tuatara from lizards, which have only one hole. The additional hole helps stabilize the skull as the tuatara bites down and spreads through the prey.

Dr. said. After a large number of statistical tests, the team identified the Navajosphenodon period near the base of the Tuatara dynasty.

The fossil shows that modern tuatara bodies appeared in the Jurassic period and changed little in 190 million years. This supports the common distinction that these remaining reptiles are “living fossils”. But Dr. Simes emphasized the differences: For example, modern tuatara’s jaws end with a set of beak-like fused teeth that are not found in navagosphenodon.

According to Kelsey Jenkins, a doctoral student at Yale who specializes in the evolution of early reptiles, many lineages of Rhynchocephalians have shown little change throughout their history. However, 200 million years is an extreme. “The only things that have been significantly preserved are things like horseshoe crabs and crickets – not reptiles of the right size,” said Ms Jenkins, who was not involved in the new study.

The researchers argue that this lack of change may represent natural selection in the case of increased velocity. “Slow rates of evolution don’t necessarily mean no evolution,” Dr. Simes said. It’s basically the evolutionary equivalent of the old saying: “If it ain’t broke, don’t fix it.”

While the discovery of Navajosphenodon helps embody a crucial chapter in tuatara evolution, much of this reptile’s back story remains hazy. Without more fossil discoveries, it will be difficult for scientists to determine why these lone survivors possessed evolutionary cheat codes.

“Why modern tuatara and their lineages have evolved so slowly for such a long period of time is a slightly larger and more difficult question,” Dr. Pearce said. “We need more excavations.”